This part of IEC 60079 is concerned with the classification of areas where flammable gas or vapour hazards could arise. The resulting classification is used as a basis to support the proper design of the installation, selection, installation, operation, inspection, maintenance and repair of equipment for use in hazardous areas.
It is intended to be applied where there could be an ignition hazard due to the presence of flammable gas or vapour, mixed with air, but it does not apply to:
a) mines susceptible to firedamp;
b) the processing and manufacture of explosives;
c) catastrophic failures or rare malfunctions which are beyond the concept of normality dealt with in this standard (see 3.8.3 and 4.7);
d) rooms used for medical purposes;
e) domestic premises;
f) where a hazard could arise due to the presence of combustible dusts or combustible flyings but the principles can be used in assessment of a hybrid mixture (refer also to IEC 60079-10-2 [22]).
NOTE 1 Additional guidance on hybrid mixtures is provided in Annex H.
Flammable mists could form or be present at the same time as flammable vapour. In such case the strict application of the details in this document might not be appropriate. Flammable mists could also form when liquids not considered to be a hazard due to the high flashpoint are released under pressure. In these cases the classifications and details given in this document do not apply. Information on flammability of mists is provided in Annex G.
Atmospheric or ambient conditions include variations above and below reference levels of 101,3 kPa (1 013 mbar) and 20 °C (293 K), provided that the variations have a negligible effect on the explosion properties of the flammable substances.
NOTE 2 Atmospheric or ambient conditions do not correspond to normal (or standard) conditions of other relevant standards (for example IUPAC standard temperature and pressure STP are related to 0 °C and 101 325 Pa).
In any site, irrespective of size, there could be numerous sources of ignition apart from those associated with equipment. Appropriate precautions will be necessary to ensure safety in this context. This standard is applicable with judgement for other ignition sources but in some applications other safeguards also need to be considered. For example, larger distances might apply for open flames when considering hot work permits.
This document does not take into account the consequences of ignition of an explosive gas atmosphere except where a zone is so small that if ignition did occur it would have negligible consequences (see 3.4.8 and 4.6.2).
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